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Amedee
Amedee, Former ASE Master Tech
Category: Car
Satisfied Customers: 25636
Experience:  ASE certified tech advanced level specialist. Wisconsin certified emissions state inspector
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1987 porsche 924: coil still not firing

Resolved Question:

1987 porsche 924 will not start .getting no fire to plugs.changed coil still not firing.
Submitted: 9 years ago.
Category: Car
Expert:  Amedee replied 9 years ago.
Greetings! With the key on, make sure there is full battery voltage at the coil and with a test light, check to see if there is a ground signal trigger when cranking. THis is the signal at the coil that starts the spark process from the coil.
Customer: replied 9 years ago.
how do I check to see if there is a ground signal trigger?
Customer: replied 9 years ago.
How do I check to see if there is a ground trigger signal?
Expert:  Amedee replied 9 years ago.
Take the alligator clip of the test light and clip it on battery positive. Take the tip of the test light and touch the other wire on the coil (not the power wire) and crank the engine over. THe test light should blink.
Customer: replied 9 years ago.
Test light does not blink @ negative side of coil while cranking.
Customer: replied 9 years ago.
Test light does not blink @ neg. side of coil while cranking.
Expert:  Amedee replied 9 years ago.

This means the computer is not seeing a crank signal.

924 & 944 Models

  1. Turn ignition Off, then remove DME ECU multiple wiring connector.
  2. Connect suitable oscilloscope to terminals 25 and 26 of ECU connector.
  3. Start engine, then observe oscilloscope tube. A single sine wave should be displayed. The oscillation should begin with a positive slope displaying at least 2 volts with a starter speed of at least 200 RPM. As engine speed increases, the display amplitude should also increase.
  4. If transmitter output is less than 2 volts, check clearance between reference mark transmitter and ring gear. Refer to System Service for procedure.
  5. If display shows no transmitter signal, proceed to step 6.
  6. Using suitable ohmmeter, measure between ECU connector terminals 25 and 26 to determine reference mark transmitter coil resistance. Resistance should be .6 - 1600 ohms.
  7. If resistance is not within specifications, replace transmitter.
Customer: replied 9 years ago.
where is ecu located on car
Customer: replied 9 years ago.
where is ecu located on car
Customer: replied 9 years ago.
where is ecu located
Expert:  Amedee replied 9 years ago.

Location
- Passenger footwell
- Under drivers seat [Carrera]

Customer: replied 9 years ago.
checked between 25 and 26 on plug on ecu this circuit is open
Expert:  Amedee replied 9 years ago.

924 & 944 Models

  1. Turn ignition Off, then remove DME ECU multiple wiring connector.
  2. Connect suitable oscilloscope to terminals 8 and 27 of ECU connector.
  3. Turn engine over with starter while observing oscilloscope tube. Sine waves should be displayed with amplitude of 2.5 volts or more from peak to peak.
  4. If amplitude is less than 2.5 volts peak to peak, check clearance between speed sensor and ring gear. Refer to System Service for procedure.
  5. If clearance between ring gear and speed sensor is satisfactory, or if pattern is not displayed or weak, proceed as follows:
    1. Using suitable ohmmeter, measure between ECU connector terminals 8 and 27 to determine speed sensor coil resistance. Resistance should be .6 - 1600 ohms.
    2. Using ohmmeter, measure between ECU connector terminals 5 and 8 to determine speed sensor insulation resistance. Resistance should be 1 M-ohm.
    3. If resistances are not within specifications, replace sensor.

Magnetic Coil Sensors

graphic

Customer: replied 9 years ago.
is this the referance mark or speed mark sensor and where are they located.thank you.........
Expert:  Amedee replied 9 years ago.

Sorry... my references do not tell me where they are located.

If my answer is not good enough, just let me know and I will leave this question open for other experts.

Thanks!

Customer: replied 9 years ago.
that would be great. I have looked on the engine front and back and have not seen a sensor for the crank.thanks.....
Expert:  Amedee replied 9 years ago.
You got it!
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